| Abstract: | The ability of Pseudomonas (Ps.) chlororaphis isolate Tx-1 to suppress Pythium aphanidermatum and control root rot was investigated in sweet peppers grown in small-scale hydroponic trough units with recirculating nutrient solution. The agent was introduced to the nutrient solution 3 days after the peppers were inoculated with P. aphanidermatum, or 4 days before and 3 days after inoculation, or 4 days before and 3 and 10 days after. Controls either received no agent or pathogen, or the agent only (applied once, 4 days before the time of pathogen inoculations), or the pathogen only. The experiment was conducted in a greenhouse with repetitions beginning in January, March, and May. Severity of root browning associated with P. aphanidermatum, in the absence of Ps. chlororaphis, increased in the first, second and third repetitions, respectively, to 74% at 21 days, 28% at 21 days, and 68% at 11 days. In treatments with one, two, or three applications of Ps. chlororaphis, respectively, areas under root browning progress curves were reduced by 18-48%, 50-73%, and 62-79% compared to the pathogen controls, and recovery incidence of the pathogen from roots at 21 days after inoculation was reduced by 14-47%, 62-82%, and 60-89%. Roots not inoculated with P. aphanidermatum were whitish and not colonized by the pathogen. Density of Ps. chlororaphis in treated plants was usually 2×103-1.2×105 cfu g-1 fresh roots. The Ps. chlororaphis treatments almost invariably prevented reductions in plant height, leaf area, fresh mass and dry mass of the shoots and of the roots, and root volume associated with P. aphanidermatum and root browning. It is concluded that Ps. chlororaphis Tx-1 strongly antagonized P. aphanidermatum in the pepper roots and that the agent has considerable potential for controlling root rot and maintaining productivity in commercial hydroponic peppers. |
